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.Dd March 12, 1998
.Dt SCHED_SETPARAM 2
.Os
.Sh NAME
.Nm sched_setparam ,
.Nm sched_getparam
.Nd set/get scheduling parameters
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sched.h
.Ft int
.Fn sched_setparam "pid_t pid" "const struct sched_param *param"
.Ft int
.Fn sched_getparam "pid_t pid" "struct sched_param *param"
.Sh DESCRIPTION
The
.Fn sched_setparam
system call sets the scheduling parameters of the process specified by
.Fa pid
to the values specified by the
.Fa sched_param
structure pointed to by
.Fa param .
The value of the
.Fa sched_priority
member in the
.Fa param
structure must be any integer within the inclusive priority range for
the current scheduling policy of the process specified by
.Fa pid .
Higher numerical values for the priority represent higher priorities.
.Pp
In this implementation, if the value of
.Fa pid
is negative the system call will fail.
.Pp
If a process specified by
.Fa pid
exists and if the calling process has permission, the scheduling
parameters are set for the process whose process ID is equal to
.Fa pid .
.Pp
If
.Fa pid
is zero, the scheduling parameters are set for the calling process.
.Pp
In this implementation, the policy of when a process can affect
the scheduling parameters of another process is specified in
.St -p1003.1b-93
as a write-style operation.
.Pp
The target process, whether it is running or not running, will resume
execution after all other runnable processes of equal or greater
priority have been scheduled to run.
.Pp
If the priority of the process specified by the
.Fa pid
argument is set higher than that of the lowest priority running process
and if the specified process is ready to run, the process specified by
the
.Fa pid
argument will preempt a lowest priority running process.
Similarly, if
the process calling
.Fn sched_setparam
sets its own priority lower than that of one or more other nonempty
process lists, then the process that is the head of the highest priority
list will also preempt the calling process.
Thus, in either case, the
originating process might not receive notification of the completion of
the requested priority change until the higher priority process has
executed.
.Pp
In this implementation, when the current scheduling policy for the
process specified by
.Fa pid
is normal timesharing (SCHED_OTHER, aka SCHED_NORMAL when not POSIX-source)
or the idle policy (SCHED_IDLE when not POSIX-source) then the behavior
is as if the process had been running under SCHED_RR with a priority
lower than any actual realtime priority.
.Pp
The
.Fn sched_getparam
system call will return the scheduling parameters of a process specified
by
.Fa pid
in the
.Fa sched_param
structure pointed to by
.Fa param .
.Pp
If a process specified by
.Fa pid
exists and if the calling process has permission,
the scheduling parameters for the process whose process ID is equal to
.Fa pid
are returned.
.Pp
In this implementation, the policy of when a process can obtain the
scheduling parameters of another process are detailed in
.St -p1003.1b-93
as a read-style operation.
.Pp
If
.Fa pid
is zero, the scheduling parameters for the calling process will be
returned.
In this implementation, the
.Fa sched_getparam
system call will fail if
.Fa pid
is negative.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
On failure
.Va errno
will be set to the corresponding value:
.Bl -tag -width Er
.It Bq Er ENOSYS
The system is not configured to support this functionality.
.It Bq Er EPERM
The requesting process doesn not have permission as detailed in
.St -p1003.1b-93 .
.It Bq Er ESRCH
No process can be found corresponding to that specified by
.Fa pid .
.It Bq Er EINVAL
For
.Fn sched_setparam :
one or more of the requested scheduling parameters
is outside the range defined for the scheduling policy of the specified
.Fa pid .
.El
.Sh SEE ALSO
.Xr sched_get_priority_max 2 ,
.Xr sched_get_priority_min 2 ,
.Xr sched_getscheduler 2 ,
.Xr sched_rr_get_interval 2 ,
.Xr sched_setscheduler 2 ,
.Xr sched_yield 2
.Sh STANDARDS
The
.Fn sched_setparam
and
.Fn sched_getparam
system calls conform to
.St -p1003.1b-93 .
